This is an ongoing project to continue a multidisciplinary study of long-term aspects of the relationship between population, agricultural land use, and the environment in the Great Plains of the United States. This region is important because the grasslands of the Great Plains cover a large part of the U.S., and are subject to environmental variability. The proposed research involves an examination of the demographic experience of the region and of changes in the environment. The theoretical basis of the project draws on many sources, and is directed toward a model of recursive change in population and environment, one in which changes in one of these factors in one time period influence the other in a subsequent time period, and so on. This project will enhance an already developed database that contains county-level information about population, land use, and environment, and their social context. New analyses will look at the demographic impact of environmental variation and change through a variety of measures, including population density, social, occupational, ethnic, age and sex structures, and the dynamics of families. Other new analyses will look at land use outcomes, including the transformation of land use from agricultural to non-agricultural. This work will use of state- of-the-art statistics that take into account spatial and temporal effects. The study will continue to validate findings and develop hypotheses with in-depth research about communities within the Great Plains. The Farm Family Study, mounted during the initial project period, will continue to provide insights about the behavior of farm families within their environmental and social contexts. One important outcome of the research will be a new overview of changing land use and agricultural technology in the Great Plains since 1880. This history will be validated with the accumulated data about population and agriculture from the censuses. The final stage of the project will be to follow these analyses with a model-building and simulation exercise that will first build long-term models of environmental change using the CENTURY soil model system. The investigators will also integrate the analysis of demographic and environmental change by building a demographic and social change component to add to the CENTURY model, and comparing the results of the modeling exercise with the historical record for the Great Plains.